A bicycle speed change assembly for sports type bicycles such as a racing bicycle is often mounted on a bicycle frame member such as the down tube or the top tube.
Therefore, the rider must unhand the handlebar to perform a speed change operation. As a result, it is impossible to immediately perform a braking operation during the speed change operation. In addition, the rider has to assume a single hand steering, which leads to unstable handlebar operation and poor safety.
The speed change operation is required mainly when road conditions change, for example, from a flat road to a slope, or vice versa. In such occasions the bicycle becomes unstable and the brake operation is often needed.
In an attempt to solve this problem the Japanese Utility Model Laid-open 58-46693, for example, discloses a speed change operation assembly, wherein a cylindrical operation member is fitted around each of the left and right grip portions of the handlebar, and these cylindrical operation members are rotated to pull or pay out respective speed control cables. This type of speed change operation assembly is commonly called a grip rotating type speed change operation assembly.
In this grip rotating type speed change operation assembly, it becomes possible to perform a speed change operation without unhanding the handlebar grip portion, resulting in remarkable improvement in riding safety.
In off-road riding on a mountain bike for example, it is sometimes necessary to perform a speed change operation at the same time with a braking operation.
In such a case, however, with the conventional grip rotating type speed change operation assembly, the cylindrical operation member must be rotated to a rotational position corresponding to a speed step. In particular, when the speed change operation is required through a plurality of speed steps, the amount of rotation required of the cylindrical operation member becomes large, and therefore, the hand and fingers must be re-positioned on the cylindrical operation member. Thus, it is very difficult to perform a speed change operation while operating the brake lever in the conventional handlebar rotating type speed change operation assembly.
In addition the speed change operation is performed in various ways in response to the changing running situation; sometimes the speed change operation is made all the way through several speed steps as mentioned earlier, or some other times the speed change operation is made in a stepped manner. It is too demanding to perform such different types of speed change operation smoothly using a cylindrical operation member disclosed in the above gazette.